An electrowetting display is an image display system which includes a substrate and, disposed thereon, a plurality of pixels filled with two phases, i.e., an aqueous medium and an oil-based coloring ink, and in which the affinity of the aqueous medium/oil-based coloring ink interface is controlled for each pixel by means of a voltage application on-off operation to spread/gather the oil-based coloring ink on the substrate and thereby display an image (non-patent document 1). The dyes for use in electrowetting displays are required to have high solubility in low-polarity solvents and high durability, e.g., light fastness (patent document 1 and patent document 2).
Patent document 2 describes a highly light-fast anthraquinone dye for use in electrowetting. In general, anthraquinone dyes have a low molar extinction coefficient and must be used in a higher concentration in order to attain an extinction coefficient substantially the same as that of heterocyclic azo dyes. As a result, higher solubility is required of the anthraquinone dyes. Furthermore, when an anthraquinone dye is used in a high concentration, an increase in viscosity and a change in electrical property occur in the electrowetting. There is hence a possibility that use of the disclosed anthraquinone dye in electrowetting applications might be problematic.
Patent document 3 describes a pyrazole disazo dye having high solubility in hydrocarbon solvents. However, n-decane solutions of the dye are yellow, and the dye does not conform to other color tones.
Patent document 4 and patent document 5 describe red heterocyclic azo dyes which are for use as thermal-transfer dyes and are akin to the dye of the present invention. However, no statement or suggestion concerning solubility in low-polarity solvents is given in the documents.